Unimolecular nucleophilic substitution (SN1), overview

TRANSCRIPT
There are two elementary steps in the SN1 reaction mechanism. The first step is the departure of the leaving group (LG). The leaving group takes the two bonding electrons as a lone pair and detaches from the carbon atom. The loss of electron from carbon confers a positive charge in the carbocation intermediate. In the second step, a lone pair from a nucleophile (Nu) forms a bond to the electron-deficient carbon and fills in the positive charge. The nucleophile can approach the carbocation in two directions, either the same face as the original leaving group or the opposite face. The product solution can have a mixture of stereochemistry.
(𝘚)-3-Iodo-3-methylhexane has iodine as the leaving group. The two bonding electrons shared between carbon and iodine is taken by iodine as a lone pair. The iodide ion diffuses away from the carbocation. Bromide ion, as the nucleophile, uses a lone pair to form a bond with the positively charged carbon atom. If the bromide ion attaches to the carbocation at the same face as the original leaving group, then the product is (𝘚)-3-bromo-3-methylhexane. If bromide attaches at the opposite face, then the product is (𝘙)-3-bromo-3-methylhexane. The product solution will have an equal mixture of (𝘚)- and (𝘙)-stereoisomers.
Original content © 2024 Jung-Lynn Jonathan Yang
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